This invention relates generally to device enclosures and specifically to a device enclosure having integrated structures providing retention, electromagnetic interference (EMI) containment and structural load distribution.
Electronic devices have grown increasingly complex. Today's devices often use computer processors operating at very fast clock cycles. Devices may process analog or digital signals that are at high frequencies, such as television, video, or other signals. In such applications, the electronics used are sensitive to, or emit, EMI. Such devices can be interfered with, or can interfere with other devices, when multiple devices are placed in proximity with each other. For example, a satellite television receiver, such as an integrated receiver decoder (IRD), or, more generically, a "set-top box," processes and emits high frequencies and can interfere with, and be affected by, devices such as cellular telephones, home computers, etc. Also, EMI can be caused by ambient electrical signals such as broadcast signals. As the home becomes populated with high frequency processing devices the likelihood of interference increases.
Not only do manufacturers of electronic devices strive to make products that will work reliably in places where EMI is present, but the amount of EMI emission is regulated by government bureaus such as the Federal Communications Commission (FCC). The FCC requires that electronic devices that might emit EMI must be certified to be below certain acceptable EMI levels.
EMI "shielding" is useful in both containing EMI in an electronic circuit, and preventing EMI from external sources from affecting the functioning of the circuit. An ideal shielding, or "shield," would be a smooth conducting surface forming a continuous and complete enclosure around the circuit, shaped and oriented according to the type of EMI to block and contain. However, such a design is not possible in the real world in real environments.
Prior art approaches have taken the approach of making the shielding part of the enclosure, or "chassis," of the housing of a device using an electronic circuit. In this approach, the design of the shielding suffers because a housing needs to perform additional functions such as mounting, protecting and supporting the components of the device. This requires that holes be made in the enclosure to allow, e.g., cables, controls, to enter and protrude from within the enclosure. Also, thermal considerations are a concern and the housing often needs to have ventilation holes. The size and shape of the housing often determines the major part of the size and shape of the overall device. An important design consideration is making the "footprint" of the device compatible with other devices or with the intended environment. A rectangular enclosure is often desirable so it can be stacked and easily moved and manipulated. However, the sharp corners of a rectangular design detract from an optimum shield. Also, the enclosure needs to be easily assembled and disassembled, first for the original manufacturing and later for servicing or upgrading. Achieving a rectangular design that is easily taken apart and put back together while at the same time provides high shielding has proven elusive.
Other considerations, such as keeping the cost of the housing low while maintaining structural integrity and maximizing the manufacturing yield of the housing, must be taken into account in the design.
Thus, it is desirable to provide a housing design providing EMI containment and shielding while, at the same time, meeting other design considerations such as ease of assembly and structural integrity.